1. Field of the Invention
The present invention relates to a flow rectifier applicable to such equipment as a head box in a paper machine where gas or liquid is fed through widthwise arrayed perforations. More particularly, slits are prepared at the outlet of the perforations, and, from these slits, gas or liquid is fed as a jet (shower) in the form of widthwise extended film.
2. Description of the Prior Art
An example of the head box in the conventional paper machine is shown in FIGS. 1(A) and (B). Referring to these drawings, the flow of the raw paper liquid and the function thereof are described herebelow. Reference numeral 1 designates a rectangular header constituting the flow path, of which the cross-sectional area is decreased while proceeding downstream to uniformly feed the raw paper liquid to a tube bank 2. Furthermore, to make uniform the flow in the widthwise direction, it is so adapted that a part of the raw paper liquid having entered into the rectangular header 1 passes by and re-circulates in the rectangular header 1. Reference numeral 2 designates a tube bank consisting of a group of tapered tubes 3, of which the tube at the inlet side 3a has a small diameter to increase the pressure loss and to obtain uniform distribution in the widthwise direction, while the tube at the outlet side 3b has a large diameter whereby the raw paper liquid enters into a killing port 4 at low speed to facilitate mixing in the flow. In addition, the latter part is given satisfactory length to change the direction of flow by 90.degree..
Reference numeral 4 designates a killing part characterized by a chamber without a partition throughout the width, aimed at making uniform the pressure and the flow. Reference numeral 5 designates a perforated plate, which functions to cause the pressure loss so that the raw paper liquid is uniformly distributed in the widthwise direction. This perforated plate 5 further functions to uniformly distribute the raw paper liquid in each converging channel 6. Reference numeral 7 is a sluice chamber, and its top plate 9 and a bottom plate 10 converge toward a sluice opening 8. The top plate 9 can rotate with the fulcrum 11 as a center, thereby the clearance at the sluice opening 8 is able to be changed. On the other hand, fine adjustment of the clearance at the sluice opening 8 in the widthwise direction is effected by mechanically flexing a sluice lip 12 by means of the jacking rods (not shown) arrayed in the widthwise direction.
Moreover, as shown in FIG. 3, in the flow following the perforated plate 5, there are a number of irregularities caused in flow speed and by the influence of the jet flow ejected from the perforations. In order to damp down these turbulences in the flow, the inner space of the sluice chamber 7 is partitioned by a plurality of sheet-like restraining elements 13, forming a plurality of converging channels 6. One end 13a of each restraining element 13 is supported on the perforated plate 5, and the restraining elements 13 are held at the same intervals by the flow of the raw paper liquid.
However, the above-mentioned equipment in the prior art had the following shortcomings. That is, it was observed by viewing the flow that there existed a slight local difference in the flow speed in the widthwise direction at the outlet 6b of the converging channel 6. Such local difference in the flow speed causes turbulence in the jet after the sluice lip 12, leading to unevenness of the thickness of the jet. Presumably, such difference in the flow speed is caused by undiminished inherent characteristics of the jet flow imparted by the influence of the perforated plate 5.
In addition, when the highly concentrated raw paper liquid is allowed to flow at low flow speed in the converging channel 6 after the perforated plate 5, as shown in FIG. 2, a plurality of triangular parts 6a with low concentration can be observed in the widthwise direction between the adjacent jets ejected from the perforations in the perforated plate 5. Such triangular parts 6a with low concentration are considered to be caused because the water readily turns into the space between the adjacent jets, while the fiber is liable to flow together with the flow of the jet core, being difficult to turn into the space between the adjacent jets. These streaks with low concentration are observed to be stretched and washed away downstream.
In the meanwhile, in order for the inherent characteristics of the circular jet ejected from the perforation into the water to vanish, the length of the jet flow is generally required to be 12 to 36 times as long as the diameter of the jet flow. When the restraining elements 13 are disposed in the sluice chamber 7, inherent characteristics of the jet flow rapidly vanish; nevertheless, it has been proved that the conventional length of the sluice chamber 7 has not been sufficient to completely make uniform the flow characteristics in the widthwise direction. On the other hand, if the sluice chamber 7 is lengthened, its characteristic frequency is decreased, inner volume of the sluice chamber 7 is changed by the vibration of the top plate 9 and the bottom plate 10, and irregularity is caused in the ejection speed of the jet.
In the head box previously proposed by the inventor, the sluice chamber 7 was lengthened, and characteristic frequency of the sluice chamber 7 was successfully increased up to the practically allowable level, but it is not desirable to further lengthen the sluice chamber 7 to eliminate the influence of ejection speeds. Meanwhile, decreasing the hole diameter of the perforated plate 5 enables the length of the sluice chamber 7 to be shortened, but possible clogging of the raw paper liquid prevents the hole diameter from being decreased to less than the current size.
Originally, uniformity of the raw paper liquid in the widthwise direction is attained by the throttling effect of the tube band 2 and the perforated plate 5. Therefore, if the opening rate of the perforated plate 5 is decreased to heighten the throttling effect, the tube bank 2 may be dispensed with, but, on the other hand, if the opening rate of the perforated plate 5 is decreased to less than the status-quo, the jet speed is increased, and the distance necessary to eliminate the inherent characteristics of the jet is lengthened. Therefore, it was found difficult to make the equipment compact by dispensing with the tube bank 2.
In the meanwhile, FIG. 21 through FIG. 23 illustrate conventional shower equipment where a shower 61 of fluid is ejected from drilled holes 47 in a pipe 46 against a travelling belt 48. FIG. 21 is a perspective side view showing the shower equipment provided in the pipe 46, and FIG. 22 and FIG. 23 are respectively a front view and a cross-section side view of the pipe 46 provided with the drilled holes 47. However, this conventional shower equipment shown in FIG. 21 through FIG. 23 had the shortcoming that the shower 61 was concentrated on the parts directly below the drilled holes 47.
FIG. 24 through FIG. 26 illustrate conventional shower equipment with a slit nozzle. In the equipment shown in FIG. 24 and FIG. 25, a slit 51 is provided in a pipe 49, and the shower 61 is ejected from the slit 51 against the travelling belt 48. In this case, however, machining of the slit 51 is difficult, and, in addition, shortcomings were found. Since the part of the slit 51 was widthwise cut, it constituted the structural weak point and machining could not obtain high accuracy. Furthermore, the opening rate was larger in this case than in the case of the drilled holes 47 and irregularity in flow rate was found in the widthwise direction between the flow-in side and the flow-out side.
In the conventional shower equipment shown in FIG. 26, an inner pipe 52 is provided inside an outer pipe 50, and a slit 53 is cut in the outer pipe 50, while holes 54 are drilled in the inner pipe 52 in the opposite direction. This conventional shower equipment consists of double pipes to reduce the irregularity in the flow rate in the widthwise direction, but also has the shortcoming that the diameter of the outer pipe 50 was inevitably increased unnecessarily.